1. Positive Temperature Coefficient (PTC): Nearly all metals used in RTDs exhibit a Positive Temperature Coefficient. This means that as the temperature increases, the electrical resistance of the metal also increases.
2. The Mechanism: In metals, as the temperature rises, the atoms vibrate more vigorously. These vibrations increase the number of collisions between the atoms and the flowing electrons, effectively creating more "friction" or resistance to the current.
3. Comparison with Thermistors:
• RTDs (Metals): Have a PTC (Resistance increases with heat).
• Thermistors (Semiconductors): Usually have a Negative Temperature Coefficient (NTC), meaning their resistance decreases as temperature rises.